<template>
    <ul class="list">
        <li class="item" 
        v-for="item of letters" 
        :key="item"
        :ref="item"
        @touchstart.prevent="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        @click="handleLetterClick"
        >
            {{item}}
        </li>
    </ul>
</template>

<script>
export default {
    name: 'CityAlphabet',
    props:{
        cities: Object
    },
    computed:{
        letters() {
            const letters = []
            for(let i in this.cities){
                letters.push(i)
            }
            return letters
        }
    },
    data() {
        return{
            touchStatus: false,
            startY: 0,
            timer: null
        }
    },
    updated () {
        this.startY = this.$refs['A'][0].offsetTop
    },
    methods:{
        handleLetterClick(e){
            this.$emit('change', e.target.innerText)
        },
        handleTouchStart() {
            this.touchStatus = true
        },
        handleTouchMove(e) {
            if(this.touchStatus) {
                if(this.timer){
                    clearTimeout(this.timer)
                }
                this.timer = setTimeout(() => {
                    const startY = this.$refs['A'][0].offsetTop
                    const touchY = e.touches[0].clientY - 79
                    const index = Math.floor((touchY - this.startY) / 20)
                    // console.log(index);
                    // console.log(startY);
                    if(index >= 0 && index < this.letters.length){
                        this.$emit('change', this.letters[index])
                    }
                },16);
            }
        },
        handleTouchEnd() {   
            this.touchStatus = false
        }
    }
}
</script>

<style lang="stylus" scoped>
@import '~styles/varibles.styl'
.list
    display: flex
    flex-direction: column
    justify-content: center   
    position: absolute
    right: 0
    top: 1.58rem
    bottom: 0
    width: .4rem
.item
    line-height: .4rem
    text-align: center
    color: $bgColor                     
</style>